The invention relates to a process of separately recovering vanadium and molybdenum from an aqueous solution containing a vanadium compound and a molybdenum compound. Such an aqueous solution is formed for instance by leaching a residue obtained by heating a composition containing vanadium and molybdenum, for example a spent desulphurization catalyst, in the presence, if desired, of substances such as sodium carbonate or sodium chloride (see the German Patent Application 2 316 837). In said German Application it is proposed to selectively extract the solution containing heavy metal with, for instance, a tertiary amine.
In addition to the general disadvantages of a liquid-liquid extraction, such as the solubility of the extraction agent in the water phase with resulting waste problems and separation problems, the above process has the disadvantage that when the extraction agent loaded with the heavy metal is stripped with, for instance, sodium carbonate, precipitation of ammonium vanadate can only be effected after the addition of a large excess of ammonium salt. Stripping with the aid of an ammonium hydroxide solution, which makes it possible in principle to avoid the additional use of ammonium salt, has the disadvantage that there is formed a precipitate which makes it very difficult to separate the aqueous phase from the organic liquid.
Further it is known that strongly basic anion exchange resins such as Amberlite IRA-400, -401, -410 and -411, Permatit S-1 and Dowex -1, -11 and -21K are used in the removal of vanadate ions from aqueous solutions which should have a particular pH-value, the elution of the resin generally being carried out with the aid of an acid or with a specific salt solution, for instance a solution of 3.4 to 4.2 moles of sodium chloride and 0.50 to 0.80 moles of ammonium chloride per liter of the eluant (see for instance the U.S. Pat. Nos. 2,937,072 and 3,376,105, and Chem. Zentrallblatt, 1960, No. 50, p. 16677).